The purpose of this project is to biochemically characterize retroviruses and retroviral and cellular onc genes in order to understand the mechanisms by which these viruses and cellular genes induce cancers. The role of these sequences in the etiology of human cancers is also under study. Studies currently in progress are the following: (1) biochemical characterization of replication-defective mammalian transforming viruses; (2) biochemical characterization of new isolates of retroviruses; (3) search for the presence of retroviral genes and gene products in human tumors; and (4) characterization of human onc genes in normal and malignant human cells.